The present invention relates to an electronic ignition timing control system adapted for electronically determining the ignition timing of four cycle internal combustion engines (hereinafter referred to as engines) having four cylinders or more.
The distributors which have heretofore been used generally for determining the ignition timing of engines are so designed that the relative position between the elements of a cam and point or electric contact assembly is varied in accordance with the magnitudes of the engine speed and the intake manifold vacuum to generate an ignition signal at the proper ignition point that suits the engine operating conditions. A disadvantage of this type of devices is that since all the controls are accomplished mechanically, the ignition timing provided cannot be fully reliable and it is also difficult to ensure an ideal ignition timing characteristic, thus giving rise to a problem from the standpoint of exhaust emission control which is now at issue.
Another type of device is known in the art in which a reference position detecting rotor disk is mounted on the shaft of the distributor so that a pickup generates a reference position signal for each cylinder in response to the rotation of the rotor disk, and the point or position at which the reference position signal was generated is utilized as a reference point to electronically determine an ignition timing corresponding to the parameters of an engine, whereby the resulting output is subjected to power amplification by an ignitor to interrupt the ignition coil and the resulting high voltage produced in the ignition coil is distributed through the distributor to the spark plugs of the respective cylinders. A disadvantage of this type of device is that since a high voltage distributing distributor is used, the distribution of high voltage by the discharge of the distributor causes noise wave, and moreover due to the fact that the distributor is driven from the engine through the gear, a play is produced by the backlash of the gear or the like thus causing an error in reference position signals and thereby deteriorating the ignition timing accuracy.